Process for extracting fixed and mineral oils

ABSTRACT

The present invention relates to a method of extracting and concentrating oils from materials in which the oils are already dispersed. More particularly, the present invention is concerned with the extraction of fixed oils or mineral oils from materials using a process of solvent extraction which is performed under elevated pressure and temperature. The solvent medium may be HFC 134a alone, or HFC 134a in combination with a suitable co-solvent which can be determined in accordance with the invention.

The present invention relates to a method of extracting andconcentrating oils from materials in which the oils are alreadydispersed. More particularly, the present invention is concerned withthe extraction of fixed oils or mineral oils from materials using aprocess of solvent extraction which is performed under pressure.

The term “Fixed Oil” is usually used to describe oils of vegetable oranimal origin which are not volatile oils. They routinely comprisenatural mixtures of mono-, di and tri-glycerides, fatty acids, sterols(and their esters) and natural waxes.

“Mineral Oil” is a term usually used to describe petrochemical oilsoften derived from below ground level, which are normally mixtures ofaliphatic and aromatic hydrocarbons of a very wide variety of chainlength and molecular weight. These oils are often the sources oflubricating and fuel oils.

In a previous patent specification (GB 2,276,392), we described the useof 1,1,1,2-tetrafluoroethane (HFC 134a or R 134a) as a solvent for theextraction of fragrant and aromatic essential oils from natural sources.The term “Essential Oil” is usually used to describe those volatile oilsof low molecular weight which incorporate the fragrance and flavour ofcomponents derived from plant materials.

However HFC 134a is in fact a very poor solvent for many compounds,particularly less volatile compounds. Thus, whilst HFC 134a is able todissolve some essential oils thereby facilitating extraction of suchoils from plant-based materials, this solvent is not able easily todissolve compounds of lower volatility such as fixed oils. HFC 134a istherefore capable of extracting only very high quality fragrant andaromatic essential oils ie delicate oils of high volatility and lowmolecular weight and it will not dissolve the fixed oils which are alsofrequently associated with these components in the natural raw material.

Furthermore, HFC 134a (which was developed in the late 1980's as arefrigerant intended to replace the environmentally unacceptableR12-dichloro difluoromethane) is so poor a solvent that it is not evenadequately miscible with or soluble in the mineral oils traditionallyused as lubricants in refrigeration compressors. This problem was sosevere, in fact, that the chemical industry was obliged to synthesisecompletely new families of lubricants for use in refrigerationcompressors in which HFC 134a was to be used as the refrigerant. HFC134a is therefore conventionally regarded as a very poor solvent.

Presently, there is no convenient and economical method of obtainingfixed oils from natural sources. The preparation of bulk commodity“fixed oils” for culinary cosmetic, food, pharmaceutical etc use,frequently from seeds and nuts such as corn (maize), ground nuts,sunflower seeds, grape pips, rape seeds, olive pits, oil palm nuts,sesame seeds, ‘evening primrose’ seeds, cocoa beans, copra (driedcoconut flesh) etc, is normally carried out in the first instance by apressing procedure. This is not a particularly efficient method ofobtaining the oils and results in significant wastage.

The seeds or other raw materials are mechanically disrupted and then theoil is squeezed out of the disrupted seed bio-mass in some form offilter press. Hydraulic, screw and continuous cavitation screw pressesare well known internationally as means of expelling such oils. The oilobtained by such pressing (in the case of olive oil, for instance) isreferred to in product for retail sale as virgin or extra virgin orcold-pressed olive oil.

Such presses, however, are only able to expel and remove a proportion ofthe fixed oils from the pressed cake. The remaining oil in the cake maybe allowed to remain there and such. “oil caked” is widely traded asanimal food. However, in some cases (for example soya, evening primroseetc) it would be economically foolish to discard the cake at this stageand steps are taken to obtain more oils from the cake by means ofsolvent extraction.

In these circumstances, the oil cake is usually stirred or otherwisedispersed and brought in contact with a countercurrent of solvent suchas hexane in which the fixed oil dissolves. In the past, benzene,dichloromethane and other good solvents for such oils have been employedfor this purpose. However, the traditional good solvents suffer thedrawback that they are frequently toxic or hazardous to health.

The solution of fixed oil in the solvent is filtered and the solvent isthen evaporated to release the oil. To achieve optimum economics, thecake may be “rinsed” several times with fresh solvent in order to removethe final traces of oil from it. After drying to remove the solvent thecake may then be sold for inclusion in animal food. However, traces ofsolvent may remain in the animal cake.

Steam injection into the oil (stripping) is frequently used as a meansof lowering much of the final residue of solvent from the oil. However,it is inevitable that a proportion of residual solvent is still presentand this is detectable in the oil derived by such processes. Thedisadvantages of the process of solvent extraction thus include the lossof solvent and the risk of fire hazards since the solvent is usuallyhighly flammable.

Moreover the loss of solvent almost always occurs as a vapour in theform of a “VOC” (volatile organic compound) which is highly undesirablefrom an environmental viewpoint because it can lead to photochemicalozone generation.

The finished product from such processes are often intended for publicconsumption and the presence of toxic or harmful residues may presentdifficulties when seeking regulatory approval of the finished product.

The evaporation of the solvent from the solution of the oil, and thesolvent recovery by condensation is expensive on account of the energycosts.

In WO95/26794, a process is disclosed which comprises contacting rawmaterial with a hydrofluorocarbon-containing solvent and separating theliquor thus obtained from the raw material. The extracted components,such as pesticides, pharmaceuticals or flavoured or aromatic oils, arethen obtained from the liquor by evaporation or distillation of thesolvent.

The present invention thus aims to provide an economical process whichis also able to provide the extracted oils in relatively high yield. Itis also an aim to provide a quick extraction process which can be usedcommercially.

It is also an aim to provide a process which is easy to run and whichdoes not require bulky or complicated apparatus. It is another aim touse a solvent which is not environmentally damaging and which does nothave any significant photochemical ozone generating potential. Such aprocess aims to eliminate or reduce the losses of solvent during theextraction process. Indeed, it is a further aim to provide a process inwhich solvent losses are minimised so that there is substantially 100%solvent recovery.

It is also an aim to avoid the risk of fire or explosion by using anon-flammable solvent system, or at least a system having asignificantly reduced risk of fire or explosion.

It is also an aim to achieve a reduction in the or the absence of anytoxic solvent residues in the final product. It is thus intended todispense with the need for the elimination of or evaporation andcondensation of large quantities of solvents.

According to one aspect of the present invention, there is a provided amethod of extracting oil from a substance, the method comprising thesteps of:

-   -   a) contacting the substance with a solvent comprising HFC 134a,        and optionally one or more co-solvents, in a sealed first        vessel;    -   b) elevating the temperature of the sealed first vessel, and        optionally causing agitation of the heated mixture;    -   c) separating the resulting solution from the substance by        transferring the solution to a second vessel;    -   d) cooling at least the second vessel to release oil from        solution; and    -   e) separating the oil from the solution.

Surprisingly, we have found that HFC 134a, though a very poor solventfor fixed and mineral oils at low temperature, is actually a very muchbetter solvent at elevated temperature. At 40 degrees Celsius forexample, cocoa butter (a fixed oil) dissolves in HFC 134a to asubstantial extent, despite the fact that at a temperature only a fewdegrees lower, ie room temperature, cocoa butter does not dissolve toany appreciable extent in HFC 134a. The reason for this significantchange in solubility of cocoa butter and other fixed and mineral oils isnot presently understood. It is however speculated that the effect maybe due perhaps to a change in the viscoelastic properties of the ‘bound’fixed oil or mineral oil at a slightly elevated temperature.

According to another aspect of the present a invention, there isprovided a sealable apparatus comprising first and second vessels, eachvessel having at least one closable value through which solvent maypass, wherein the first and second vessel are in fluid communicationwith one another by means of the closable valves, wherein the firstvessel is adapted to receive a substance from which oil is to beextracted and incorporates a filtering device to prevent passage of thesubstance out of the first vessel through the or each valve, and whereina solvent comprising HFC 134a together with one or more optionalco-solvents is provided in the first vessel and may be transferredbetween the first and second vessels via the or each valve.

In an embodiment, the or each valve is a one way valve and the first andsecond vessels each have an inlet valve and an outlet valve, theapparatus being arranged in the form of a circuit so that the outletvalve of the first vessel is connected to the inlet valve of the secondvessel, and the outlet valve of the second vessel is connected to theinlet valve of the first vessel, so that the flow of solvent around thecircuit occurs in one direction only.

In another embodiment, the first vessel is provided with a heating meansand/or is associated on its inlet side with means for heating incomingsolvent.

In a further embodiment, the second vessel is provided with coolingmeans and/or is associated on its inlet side with means for coolingincoming solution.

In a further embodiment the apparatus includes a reservoir of additionalsolvent and means for introducing or removing solvent from the circuit.Preferably, the point of addition or removal of solvent from the circuitis between the outlet side of the second vessel and the inlet side ofthe first vessel.

In another embodiment, the apparatus includes means for withdrawing fromthe second vessel directly and/or from the inlet side of the secondvessel oil which has separated from the solvent.

In a further embodiment, the apparatus includes means for determiningthe pressure in the circuit and/or the temperatures of the first andsecond vessels.

In a further embodiment, the first and second vessel's are transparentpressure vessels capable of withstanding pressures of not more than 25bar.

HFC 134a is a very poor solvent at ambient temperature as discussedabove. At elevated temperatures its dissolving properties are improvedsomewhat but they are still relatively poor. Some solutes (such as fattyacids and triglycerides) are only slightly soluble even in hot HFC 134aie a temperature of about 40 to 60° C.

In an embodiment of the process of the present invention, the solventmay be a mixture of HFC 134a and a co-solvent in which the desired oilis relatively soluble. The dissolving properties of HFC 134a aresignificantly increased by the addition of a co-solvent.

Suitable co-solvents which can be added to HFC 134a may be liquids atroom temperature or liquefied gases.

For example, hydrocarbons such as the alkanes, benzene and its esters,low boiling aliphatic esters such as acetates and butyrates, ketonessuch as acetone, methyl isobutyl ketone, methyl ethyl ketone,chlorinated, fluorinated and chlorofluorinated hydrocarbons such asdichloromethane and dichloro difluoromethane, ethers and such asdimethyl ether and diethyl ether, dimethyl formamide, tetrahydrofuran,dimethyl sulphoxide, alcohols such as methyl alcohol, ethyl alcohol,n-propanol, isopropanol, acids such as acetic acid, formic acid and evenacetic anhydride, nitrites such as acetronitrile (methyl cyanide),anhydrous liquefied ammonia and other liquefied gases such as sulphurdioxide, nitric oxide, nitrogen dioxide, nitrous oxide, liquefiedhydrogen sulphide, carbon disulphide, nitromethane, and nitrobenzenecould all be used in this process.

Liquefied gases are preferred for ease of recovery of the extracted oil.These also have the benefit of resulting in low residue levels in bothoil and spent raw material.

It is also important that the co-solvent does not damage theraw-material or the extract chosen and that the co-solvent is not toxicor hazardous to health. For this reason, lower alkanes and loweralcohols (ie C₅ or lower), acetone, dimethyl ether and diethyl ether areparticularly preferred as co-solvents.

One example of the use of a solvent mixture is in the extraction ofground nut oil. Ground nut oil does not appreciably dissolve in HFC 134aalone even at 60 degrees Celsius (when its vapour pressure is of theorder of 16 bar).

Ground nut oil readily dissolves in liquid butane at ambienttemperature. However, this fact is of little value in an extractionprocess because a solution of ground nut oil in liquid butane may becooled to very low (sub-zero) temperatures and still the solute will notprecipitate from solution. There is also a fire risk with the use ofbutane. However, a carefully chosen mixture of a co-solvent, such asliquid butane, and HFC 134a, which is tailored to the particularrequirements of the extraction process may be used in the process of thepresent invention.

The appropriate co-solvent and HFC 134a:co-solvent ratio is determinedas follows.

A bottle together with a removable seal is weighed and the weightrecorded (Weight A). This assembly should be designed to be able towithstand a pressure of say 10 BarG.

Into the bottle is placed a sample of the solute-containing raw materialto be extracted.

The bottle and seal is weighed again and the weight recorded (Weight B).The bottle is then closed and sealed. The difference between weight Band A is the weight of the solute.

The co-solvent alone is introduced into the bottle and the mixtureshaken until the contents are homogenuous and the solute is in completesolution. The bottle and contents are weighed again and the final weightof the bottle and contents are recorded (Weight C). The differencebetween weight 9 and Weight C is the weight of the added co-solvent.

HFC 134a is then progressively introduced into the bottle. At first noobvious change takes place, but as the quantity of HFC 134a increased,the contents of the bottle will be seen to turn from crystal clear toopalescent.

The weight of the bottle and contents is again recorded (Weight D). Thedifference between Weight D and Weight C is the quantity of HFC 134aadded.

In order to ensure that the composition has reached its optimum, thebottle may now be placed in a refrigerator, whereupon the contents willbecome cloudy and a clear and distinct layer of oil will separate andfloat on the lower layer of clear solvent. The solvent at lowtemperature can then be withdrawn and introduced to another bottlecharged with more of the solute-containing raw material. This coldsolvent will not dissolve the solute, but on warming, it will be seen toform a homogeneous solution (which will itself separate again into twolayers on cooling).

If this procedure is carried out carefully, it will allow calculation ofthe composition of a solvent mixture. For example: The total weight ofsolvent used is D−B. the weight of cosolvent is C−B and the weight ofHFC 134a is D−C.

Hence the weight % composition of the solvent is:Co-solvent=(C−B/D−B)×100%HFC 134 a=(D−C/D−B)×100%

The % concentration of solute in the solution=(B—A/D−A)×100%

EXAMPLE

A 210 ml capacity PET bottle (to which an aerosol valve can be removablyfitted) was weighed. The assembly weighed 48 grams.

Into the bottle was placed a sample of sunflower seed oil. The assemblynow weighed 67 grams. Hence there was 19 grams of sunflower seed oil init. The bottle was sealed.

Liquid butane was introduced into the bottle (via the aerosol valve) andweighed again. It now weighed 97 grams. Hence 30′ grams of liquid butanehad been introduced. The contents of the bottle (on shaking) werecrystal clear.

HFC 134a was now introduced into this mixture. When the bottle weighed163 grams, the contents became an opalescent but otherwise homogenous(single phase) liquid. 66 grams of HFC 134a had been added.

Placing this bottle in a refrigerator at 4 degrees Celsius for half anhour caused two layers to form. The top layer was a pale yellow oilyliquid and the lower one a water white clear liquid.

Standing at room temperature for a few minutes caused the contents ofthe bottle to warm up and (on shaking), the contents again became anopalescent homogeneous single phase liquid.

The composition of the solvent was (from the above quoted figures) 38%butane, 62% HFC 134a and the weight concentration of sunflower seed oilin solution in this solvent was 20%.

The invention will now be described with reference to FIG. 1 which showsan apparatus suitable for continuous extraction of fixed and mineraloils according to one embodiment of the process of the presentinvention.

Two vessels (1) and (2) equipped with closeable valves were coupledtogether via two sets of tubing (3, 4). Both vessels are capable ofwithstanding pressure typically up to 25 bar. Below vessel (1), thetubing (3) was in the form of a coil (5) sitting in a bath of liquid (6)which could be heated and maintained at a pre-selected temperature. Thecoil of tubing (5) could, however, be heated by another means or vessel(1) could be heated directly.

Vessel (1) was equipped with an internal filter (7) at both ends,whereas vessel (2) was equipped with a filter (8) only at the lower end.The second vessel (2) was surrounded by coils (9) containing a flow ofcooling liquid and the outside of the coils was insulated. Other meansof cooling vessel (2) could also be used, for example a stream ofcooling gas or a cooling bath.

The circuit was furnished with an inlet (10) and outlet (11) valves forsolvent. During operation of the equipment, the inlet valve was coupledto a solvent reservoir (12) which could be used to both fill and thesystem with solvent and maintain the level of solvent during operation.Outlet valve (11) was provided to enable the system to be drained.

At the tope of vessel (2), a valve (13) is fitted to facilitate therecovery of oil when this becomes necessary desirable. A pressure gauge(16) may be provided in the circuit.

The operation of the equipment may be described as follows:

-   1. vessel (1) (which has removable end caps) is charged with the    material from which oil is to be extracted (usually in the form of a    finely divided particulate solid). The end caps and filters are then    replaced. The vessel is then connected to the remainder of th    equipment.-   2. The equipment (now fully sealed) is then fully charged with    solvent from the bulk solvent storage tank (12) (which remains    connected to the equipment throughout the operation). Air is allowed    to escape from the equipment via controlled opening of the valve    (13).-   3. The hearing bath (6) is then filled with water or oil and the    heating means turned on.-   4. Cold liquid or gas is circulated round the cooling coils (5)    causing the temperature of the second vessel (2) (and its contents)    to cool.

As the temperature of the liquid in the heating bath rises, so does thetemperature of solvent in the tube below vessel (1). This, of course,causes hot solvent in vessel (1) to rise through the contents of thevessel (1) due to natural convection. The contents of vessel (1) arerestrained inside vessel (1) by the filters (7) disposed at the top andbottom. The liquid displaced upwards is replaced by cold liquid fallingthrough vessel (2) due to convection.

The entire liquid in the circuit thus becomes mobile and circulating. Ashot liquid passes up through the contents of vessel (1) oil is exactedfrom this material. As the solution enters the top of vessel (2) it iscooled and its solute (the oil) precipitates out of solution.

Because the oil is lighter than the solvent, it floats to the top ofvessel (2) and collects there as it is not able to pass out of thebottom of vessel (2).

When it is considered that sufficient oil has been extracted, all thevalves are closed except valves (14) (the inlet valve for vessel (2))and valve (15) (the outlet valve for vessel (2)). Valve (13) is thusopened to release the oil and the oil can be decanted into a bottle.

The system may be emptied after use by allowing solvent to drain out ofvalve (1) into a suitable container for recover by evaporation andre-cycling.

It will be immediately apparent to one versed in the art, that thisprocess is capable of producing oil without any evaporative step. Sinceevaporation of the solvent is one of the major costs involved in moretraditional methods of extraction, this constitutes a major improvementin the extraction of such oils and represents a significant cost saving.

Since the solvent is neither flammable, nor toxic, nor environmentallydamaging and (in normal operation) is never released into theenvironment, the process of the present invention represents asignificant improvement over current technologies.

In another embodiment of the process (not shown), the apparatuscomprises two sealable vessels (which are preferably transparent andmade of strengthened or reinforced glass) each being capable ofwithstanding a pressure of up to 20 bar or even 25 bar. Each vessel isequipped with a closeable valve which acts as an inlet and an outletvalve. One vessel is also equipped with a removable filtering device,such as a wire gauze or wire wool to prevent the exit of raw materialfrom the vessel at the same time as the solvent is withdrawn.

The two vessels are connected to each other via their inlet/outletvalves so as to form a sealed unit. Typically each vessel is 50 mls to2000 mls capacity, and preferably 100 mls to 500 mls. Such an apparatusis easily assembled and handled. However, there are no particularlimitations other than the usual practical limitations, on the uppersize of such apparatus.

In use, raw material is placed in the first vessel and the extractionmedium (ie the solvent) is also introduced into the first vessel. Theinlet/outlet valve of both vessels are then closed and the ensemble iswarmed, typically to 40°-60° (and preferably not more than 50° C.), inan oven or using other suitable heating means. The apparatus may beagitated during heating or may contain agitation means such as amagnetic flea.

After an appropriate residence time at the elevated (holding)temperature, typically in the range 1 to 20 minutes and preferably inthe range 3 to 8 minutes from the point of view of efficiency and costeffectiveness, the solution is transferred from the first vessel to thesecond vessel and the ensemble is cooled to room temperature or lower.Ideally, the ensemble is cooled to a temperature in the range −10 to 25°C. and preferably in the range 0° to 20° C. Cooling below −10° C. ispossible but increases the costs and complexity of the process.

Transfer of the solution is achieved via the inlet/outlet valves and theraw material remains in the first vessel on account of the filter. Thevalves are closed following transfer of the solvent and before coolingis commenced.

On cooling, the extracted oil precipitates out of solution and begins toaggregate. Since the extracted oil is invariably significantly lessdense that the solvent medium the extracted oil floats on the top of thesolvent layer as a separate immiscible/insoluble layer. The extractedoil can thus be easily separated by decanting. The solvent, which isalmost entirely free of the oil, can then be returned to the firstvessel for use in a further extraction cycle. This process can berepeated several times if desired. From a practical point of view, 10cycles is the upper limit with 3 to 5 cycles being preferred on thebasis of efficiency and time.

This manual procedure, though highly effective, was somewhat tedious tocarry out and the whole process is preferably performed as a continuousoperation as described above.

The present invention will now be illustrated be means of the followingExamples in which Example 1 described the isolation of a fixed oil andExample 2 describes the isolation of a mineral oil. The proceduresdescribed in these Examples are, of course, applicable to other fixedand mineral oils.

Example 1

A sample of 20 grams of roasted and finely ground cocoa beans (as rawmaterial) was placed in a transparent sealable container furnished witha closeable valve. The container was capable of withstanding pressuresof 20 bar. The in/outlet valve of the container was equipped with afilter to retain ground-up bio-mass (the raw material) within this firstvessel. 50 grams of HFC 134a was introduced into the vessel and thevessel was then a sealed. A slurry was formed between the cocoa beansolids and the HFC 134a.

A second (empty) transparent vessel which was similar to the firstvessel was prepared and the two vessels were connected by means of theirinlet/outlet valves. The valves of both vessels were both closed.

The two connected vessels, one containing the slurry and HFC 134a andthe other empty, were then placed in an oven until the temperature ofthe contents rose to 50 degrees Celsius.

When the two vessels had warmed up to 50 degrees Celsius, the valveswere opened so that the warm HFC 134a was able to pass from the vesselcontaining the bio-mass to the empty vessel. The valves were thenclosed.

The transfer and collection of the clear warm HFC 134a was readilyaccomplished via the filters. No boi-mass was present in the clearsolution which had been transferred to the second vessel.

Both vessels were allowed to cool.

Upon cooling of the HFC 134a, it was observed that cocoa butter (iecocoa oil) had precipitated out of solution as a flocculent whiteprecipitate.

Furthermore, due to the difference between the specific gravity of the“oil” (which in most cases is substantially lower than 1.00) and thesolvent (which is substantially greater than 1.2) the precipitate wasseen 7 to rise to the surface of the (now cold) HFC 134a solvent leavinga clear layer of HFC 134a below it. A small amount of furtherprecipitation of cocoa butter solids could be encouraged byrefrigeration of the second vessel containing the HFC 134a.

Recovery of the HFC 134a layer was achieved either by decantation or byfurther filtration.

The cold solvent layer which then contained substantially no dissolvedcocoa oil could then be returned to the vessel containing the originalground cocoa bean bio-mass and/or new bio-mass to be re-used in theextraction process.

When the first vessel was again warmed more cocoa butter could beextracted into the solvent, the solvent transferred is the second vesseland cooled.

This cycle was repeated several times and a substantial amount of cocoabutter concentrated in the second vessel. The roasted and ground cocoabeans in the first vessel were largely devoid of cocoa butter after onlya few cycles (about 5).

Example 1

A sample of North Sea drilling mud comprised a highly acidic moistpowder of finely ground mineral particles, water and oil. In the past,mud of this type has been jettisoned from the drill platform directlyinto the sea. This practice is coming under close scrutiny forenvironmental reasons as it is very damaging to the local environment.

The process of the present invention allows recovery of some of thecontaminating oil from such slurries. Disposal of the treated residueinto the sea could then be allowed to continue without damage to theenvironment. The value of the oil recovered could help off-set the,inevitable on-costs of treatment.

100 grams North Sea drilling mud was loaded into a 1 liter vessel suchas that described as vessel A in FIG. 1. An entire system as illustratedin FIG. 1 was then assembled and sealed and filled with solvent which inthis case was a mixture of HFC 134a (90% w/w) and butane (10% w/w)].

The temperature of the contents of vessel A was allowed to rise to about50° C. as the contents of vessel B were cooled to about 0° C. Solventcirculated quickly around the system and a pale yellow oil began toaccumulate at the top of vessel B.

After 20 minutes of operation at equilibrium conditions (after stabletemperatures had been achieved in vessels (1) and (2), the system wassystem was shut down. All valves (except valves (14) and (15) and thebottle shut-off valve (10) were closed. Upon opening of valve (13),solvent emerged and was collected in a bottle. Opening of valve (14)also caused solvent to emerge into the bottle. In so doing, the layer ofoil in vessel (2) was observed to rise. As oil emerged through valve(13), it was collected into a second sample bottle.

A small quantity of solvent was seen to “boil-off” the oil sample. On alarger scale, this solvent could have been recovered and re-used.

The oil was found by analysis to be of excellent (light) and saleablequality.

The present invention thus addresses many of the disadvantages listedabove and provides a means of obtaining fixed oils and mineral oils ingood yields in a form approaching 100% purity. The following pointsrelate to practical operating matters for the process of the presentinvention:

Temperature Difference Between Vessels (1) and (2)

For maximum economic use of equipment designed to prepare extracts suchas those of interest to us, it is beneficial to operate vessels (1) and(2) at widely dissimilar temperatures. (The difference between thesetemperatures is commonly referred to as “ΔT”). The larger the “ΔT” thebetter the equipment will perform.

However, limits on “ΔT” are imposed by the design and fabrication of theequipment.

Upper Limit of Operating Temperature of Vessel (1)

When HFC 134a is used, whether mixed with another solvent or not, a risein the temperature of operation of Vessel (1) will automatically causean increase in the pressure (vapour pressure) within the sealed system.Indeed, the highest operating temperature of vessel (1) must obviouslynever exceed and be less than the “critical temperature” of the solvent(mixture) in use.

Also this highest operating temperature would be limited to atemperature above which damage to the raw-material or the extract mightoccur.

Lower Limit of Operating Temperature of Vessel (2)

The operating temperature of Vessel (2) must be as low as can beconveniently arranged. Sub-ambient and even refrigeration temperaturescan be used.

The lower limit of operation of Vessel (2) will be determined by thecharacteristics of the solution (and its ability to dissolve solute).The solute must dissolve in the solvent as “poorly” as can be arrangedand the “poverty” of this dissolution can be enhanced by lowering thetemperature of operation of Vessel (2). The low limit is also governedby the viscosity of the resulting oil since at very low temperaturessome oils may become difficult to handle.

1. A process of extracting oil from a substance comprising the steps of: a) contacting the substance with a solvent comprising HFC 134a, and optionally one or more co-solvents, in a sealed first vessel; b) elevating the temperature of the sealed first vessel, and optionally causing agitation of the heated mixture, to allow for the oil to be extracted from the substance to the solvent, wherein a solution is formed comprising the oil, the solvent and one or more optional co-solvents; c) separating the solution from the substance by transferring the solution to a second vessel; d) cooling at least the second vessel to allow for the oil to precipitate from the solution; and e) separating the oil from the solution.
 2. The process of claim 1, wherein the co-solvent is liquid at room temperature.
 3. The process of claim 1, wherein the co-solvent is selected from the group comprising: hydrocarbons; low boiling aliphatic esters; ketones; chlorinated, fluorinated and chlorofluorinated hydrocarbons; ethers; dimethyl formamide; tetrahydrofuran; dimethyl sulphoxide; alcohols; carboxylic acids; acetic anhydride; nitrites; anhydrous liquefied ammonia; liquefied sulphur dioxide; nitric oxide; nitrogen dioxide; nitrous oxide, and hydrogen sulphide, carbon disulphide, nitromethane, and nitrobenzene.
 4. The process of claim 3, wherein the co-solvent is selected from the group comprising: alkanes; benzene and its esters; acetates and butyrates; acetone; methyl isobutyl ketone; methyl ethyl ketone; dichloromethane; dichloro difluoromethane; dimethyl ether; diethyl ether; methyl alcohol; ethyl alcohol; n-propanol; isopropanol; acetic acid; formic acid; and acetonitrile (methyl cyanide).
 5. The process of claim 3, wherein the co-solvent is selected from the group comprising: lower alkanes, lower alcohols having 5 carbons or less, acetone, dimethyl ether and diethyl ether.
 6. The process according to any one of claims 1-5, wherein the sealed first vessel is heated to a temperature of from 40 to 60° C., inclusive in step (b).
 7. The process according to any one of claims 1-5, wherein the second vessel is cooled to a temperature in the range −10° to 25° C., inclusive, in step (d).
 8. The process of claim 1, wherein the substance is selected from the group comprising: seeds, nuts, ground nuts, oil shale and mud. 